When he speaks to America tonight, Paul Ryan will need to use a second language. His native tongue — conservatism — won’t suffice. Mitt Romney’s young running mate is a product of the Republican right’s think tanks and salons; his austere budget plans reflect the goals of the GOP’s idea factory. He dazzles conservative audiences at small dinners and large gatherings. Rush Limbaugh recently declared that Ryan had given one of the best speeches ever to the Conservative Political Action Conference, an annual confab of ideological foot soldiers. In the speech Ryan stirred the troops by name-checking the conservative economist F.A. Hayek, and he spoke in grandiose terms about transforming the role of government in America.

But prime time is not the moment for grand ideological ambition. A running mate’s convention speech is an opportunity to speak to the entire country — especially to moderate independent voters still making up their mind. So in a sense, Ryan may need to be a paler version of his true self. A man known and chosen for his long-term budget-cutting vision can’t ignore budgets entirely, of course. But neither can Ryan afford to speak in detail about his plan to transform the cherished entitlement of Medicare into a voucher-style system. Or to explain how deeply he would cut popular domestic spending programs to make his budget math add up. Instead, Ryan will likely speak more generally about the size and role of government, skimming over the hard sacrifices such a shift will require (especially from those at lower income levels).

He’s also bound to humanize himself. Plenty of Americans don’t know much about the Wisconsin Congressman. But some may know him as the author of budget plans that Barack Obama says are exercises in heartless “social Darwinism” that could leave seniors unable to afford Medicare coverage. Ryan’s best weapon against those critiques is his own life.

Romney faces a problem of heritage. He was born to privilege and amassed great wealth as an adult. He has an air of aristocracy to him — one that cramps his ability to win over middle-class voters looking for the candidate who best understands their troubles.

Ryan comes from humbler origins. It’s true that his Janesville, Wis., family was one of the area’s most prominent and well-connected families, and that Ryan is now a multimillionaire. But he still speaks effectively about living a Catholic middle-class life that is far closer to the typical American experience than Romney’s. He has already begun doing that on the campaign trail, with his references to being a proud “Catholic deer hunter.” This also affords him an opportunity to attack Obama as a cultural snob. “I’m happy to be clinging to my guns and my religion,” Ryan said at a recent rally in Pennsylvania. That kind of language has powerful appeal to the ethnic working-class voters who are crucial to the campaign’s success, some of whom respond to cultural cues as much as economic ones.

Countering his image as a coldhearted budget cutter will also require Ryan to show himself as a caring and empathetic family person. Doing so will likely mean telling the country about his parents. Ryan has already campaigned with his mother Betty, whom he invokes when talking about Medicare to demonstrate to senior citizens that they can trust him to protect their medical benefits. (“She planned her retirement around this promise,” Ryan said during a campaign visit to a Florida senior community earlier this month, during which she joined him onstage. “That’s a promise we have to keep.”)

Even more powerful is the story of Ryan’s father, who died of a heart attack when his son was just 16 years old. Ryan found his lifeless father, and says the experience seared in him the fleeting nature of life. While it’s the kind of loss no one would ever wish for, it’s also a story that helps humanize Romney — and will surely offer his national audience a note of drama they are likely to remember for the rest of the campaign.

Ryan has loads in common with the silver-haired elder atop his ticket. Ryan and Romney are number crunchers, men driven more by the power of data and market-centric theories of government than by the theater and raw emotion of politics. But politics is ineffable and often irrational, and the (disputed) rationality of the Path to Prosperity budget proposal is a hard thing to convey in a nationally televised speech before a roaring crowd. So tonight we will meet Paul Ryan, the observant Catholic, the loyal son, the witness to tragedy. We will see whether he can speak the emotional language that national politics demands.